The Substrates that support bacterial growth and the endproducts of bacterial fermentation must change during early life since the colonic microbial population and the available nutrients vary over the first three weeks of life. The aim of this study is to determine whether the absorptive preferences of colonocytes for luminal substrates match the changing metabolic products made available by bacterial fermentation, and thus maximize energy salvage for the newborn. Two groups of newborn piglets age 0 - 7 days and 14 - 21 days of age will be used to compare mucosal function. The former represents the earliest bacterial populations, and the latter an established anaerobic flora. Four techniques will be used to access colon function: 1. In vivo perfusion of the right and left colon simultaneously with electrolyte solutions containing lactose or a mixture of short chain fatty acids. 2. In vitro studies on isolated colonotyes and on fecal homogenates. 3. In vitro studies on flat sheets of colonic mucosa mounted in using flux chambers. 4. Fecal water analysis for luminal contents. These studies are designed to determine the absorptive characteristics of colonic epithilea in vivo and in vitro. They dare expected to provide needed information on the development of absorptive function in biologically distinct segments of colon. These studies will provide a basis for understanding mechanisms or energy salvage in the colon of newborns, and will clarify bacterial and host interaction in the newborn period.